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Just as with all HI/LO 16-bit partial relocations the newly-introduced MIPSr6 PC-relative R_MIPS_PCHI16 and R_MIPS_PCLO16 relocations require pairing for correct borrow propagation from the low part to the high part with REL targets, another case for PR 19977. Unlike with absolute relocation, there is a complication here in that both parts represent a calculation that is relative to the PC at the individual relocation's location rather than both referring to the location of the R_MIPS_PCHI16 relocation, normally applied to an AUIPC instruction, the location of which is used for the run-time calculation executed by hardware. To take this semantics into account, the addend of the R_MIPS_PCLO16 relocation matching a given R_MIPS_PCHI16 relocation is expected to be adjusted in the source assembly file for the distance between the two relocations in a single pair, so that once both relocations have been calculated by the linker, the expression calculated at run time is such as if the combined 32-bit immediate was added at the location of the AUIPC instruction. So for matching R_MIPS_PCHI16 and R_MIPS_PCLO16 relocations into pairs GAS needs to check for the distance between the two relocations to be equal to the difference between the addends supplied, and then the linker has to subtract the low part of the distance between the two relocations from the low part in calculating the high part, so as to factor in any borrow. A further complication is that `_bfd_mips_elf_lo16_reloc' handler is supplied with the addend differently depending on whether it has been called by GAS via `bfd_install_relocation', or by the generic linker via `bfd_perform_relocation'. In the former case the addend is supplied with the relocation itself while in the latter one it comes from the field being relocated. We currently ignore the addend supplied with the relocation and it works for calculating absolute high-part relocations, because the same addend has been previously supplied with them when `_bfd_mips_elf_hi16_reloc' was called, however this approach does not work for the PC-relative case because as noted above the low-part addend is different and we need to consistently apply the distance adjustment both with GAS and LD. Since the supplied addend and one retrieved from field being relocated won't ever be both nonzero, just use the sum of the two values. The low-part addend in `mips_elf_add_lo16_rel_addend' always comes from the field being relocated, so there's no complication there, we just need to apply the same adjustment. New linker test cases verify that the same ultimate machine code is produced both for ELF and S-record output formats, ensuring that the both the MIPS/ELF linker and the generic linker behave in the correct way, consistent with each other.
README for LD
This is the GNU linker. It is distributed with other "binary
utilities" which should be in ../binutils. See ../binutils/README for
more general notes, including where to send bug reports.
There are many features of the linker:
* The linker uses a Binary File Descriptor library (../bfd)
that it uses to read and write object files. This helps
insulate the linker itself from the format of object files.
* The linker supports a number of different object file
formats. It can even handle multiple formats at once:
Read two input formats and write a third.
* The linker can be configured for cross-linking.
* The linker supports a control language.
* There is a user manual (ld.texi), as well as the
beginnings of an internals manual (ldint.texi).
Installation
============
See ../binutils/README.
If you want to make a cross-linker, you may want to specify
a different search path of -lfoo libraries than the default.
You can do this by setting the LIB_PATH variable in ./Makefile
or using the --with-lib-path configure switch.
To build just the linker, make the target all-ld from the top level
directory (one directory above this one).
Porting to a new target
=======================
See the ldint.texi manual.
Reporting bugs etc
===========================
See ../binutils/README.
Known problems
==============
The Solaris linker normally exports all dynamic symbols from an
executable. The GNU linker does not do this by default. This is
because the GNU linker tries to present the same interface for all
similar targets (in this case, all native ELF targets). This does not
matter for normal programs, but it can make a difference for programs
which try to dlopen an executable, such as PERL or Tcl. You can make
the GNU linker export all dynamic symbols with the -E or
--export-dynamic command line option.
HP/UX 9.01 has a shell bug that causes the linker scripts to be
generated incorrectly. The symptom of this appears to be "fatal error
- scanner input buffer overflow" error messages. There are various
workarounds to this:
* Build and install bash, and build with "make SHELL=bash".
* Update to a version of HP/UX with a working shell (e.g., 9.05).
* Replace "(. ${srcdir}/scripttempl/${SCRIPT_NAME}.sc)" in
genscripts.sh with "sh ${srcdir}..." (no parens) and make sure the
emulparams script used exports any shell variables it sets.
Copyright (C) 2012-2025 Free Software Foundation, Inc.
Copying and distribution of this file, with or without modification,
are permitted in any medium without royalty provided the copyright
notice and this notice are preserved.